What is it like to de-ice an astronomical telescope millions of kilometers away?

"The de-icing program should restore and preserve Euclid's ability to collect pristine galactic starlight, but this is also the first time we have conducted this procedure."

De-icing? For space telescopes?

Image of the space agency's "dark universe survey" spacecraft Euclid, ready to go into full science mode. (Image credit: ESA) Just as drivers scrape ice off their windshields in the winter, the space agency's (ESA) Euclid Observatory is trying to de-ice astronomical telescopes millions of kilometres away.

The Euclid telescope's mirrors have been coated with a layer of ice as thick as the width of a strand of DNA, a spokesperson said in a statement on Tuesday, March 19. Although the ice is thin, its presence has caused a "small but gradual decrease" in the telescope's ability to capture large amounts of starlight. Scientists are beginning to remove the ice by heating low-risk areas of the spacecraft's optics while the telescope conducts science observations. The spokesperson said that water melting in low-risk areas of various parts of the telescope will not damage other parts.

"The de-icing process should preserve Euclid's ability to collect starlight from the original galaxy, but this is the first time we've done this process, and although we can roughly guess where the ice is, it still needs to be confirmed specifically," said Mitsuko Nakajima, a Euclid scientist at the University of Berlin in Germany.

This problem is not uncommon for space telescopes. Scientists know that it is almost impossible to prevent any water from entering the spacecraft during assembly, so "it was expected that this water would accumulate and contaminate Euclid's view," ESA said in a statement on Tuesday.

Shortly after Euclid was launched last July, scientists used an onboard heater to heat the telescope in an attempt to evaporate most of the water molecules that were present inside the spacecraft before launch. But it seems that a significant portion still entered the telescope's multi-insulation layer and dispersed when it reached the vacuum environment. In the cold vacuum environment, these water molecules tend to condense on the surface of the space telescope's mirror.

The mission team first discovered the problem when they saw a gradual decrease in the starlight they measured using one of Euclid's two science instruments, the Visible Light Instrument (VIS). To measure 1.5 billion galaxies and their star populations, VIS collects visible light from these stars in a similar way to a smartphone camera, but with 100 times more pixels. The resolution of VIS is equivalent to that of a 4k screen.

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"Some stars in the universe vary in brightness, but the vast majority remain constant over millions of years," Michail Hirmer, a Euclid scientist leading the de-ice mission, said in the statement. "So when our instruments captured a picture of a starlight that was fading slightly, we realized it wasn't the stars that were causing it, it was us."

The simplest solution would be to heat the spacecraft, mission scientists say, but that would also heat up the telescope's mechanics, causing its components to expand and not necessarily return to their original state even a week later. That would limit Euclid's field of view and, by extension, affect the quality of data it collects. Telescopes are affected by even the slightest temperature changes. So Hillmer and her colleagues plan to heat low-risk Euclid optical components first. They'll start with two mirrors that can be heated independently of each other, and then monitor how that affects the amount of light collected by VIS.

The icing problem is the second one the telescope has run into. Last September, a sensor the telescope uses for navigation mistakenly labeled cosmic rays as stars, meaning that the star patterns the telescope relies on to point to a specific area of ​​the sky could not resolve the stars. A month later, that problem was fixed.

For this latest problem, scientists expect Euclid to continue releasing small amounts of water over its six-year lifespan in orbit, so if their de-icing campaign is successful this time, the same procedure could keep Euclid's systems ice-free for subsequent missions.

BY:Sharmila Kuthunur

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